The present invention relates to aceptabular cup of the type used with hip joint prostheses.
Such an acetabular cup having a support ring is disclosed in EP-A2-0,065,482. These prosthesis components are screwed without prior cutting into the acetabulum socket by means of a screwing tool and there have a firm seat which is sufficient for early mobility of the patient. A plastic socket can be snapped into the interior of the support ring so as to serve as a bearing for the joint ball.
The prior art support ring is screwed into the outer cortex layer of the acetabulum.
The prior art socket equipped with a self-tapping support ring is provided with a polyethylene inner socket whose cap is supported in the acetabulum through the upper ring opening. The ring structure of the support ring makes it possible for the latter to adapt itself by appropriate deformation to local conditions in the acetabulum so that threaded engagement and the introduction of forces is physiologically possible without excess local stresses on the bone structure. In this way, any bone catabolism, in particular, is avoided as it otherwise occurs in the region of local force peaks.
On the other hand, artificial hip sockets are known which are closed metal hemispheres. These sockets have the drawback that, due to their greater stiffness, they are unable to adapt themselves to the acetabulum when they are being screwed in.